Although networks like the Internet have been in existence for years, they have not been a popular medium of information exchange until very recently. The recent explosive growth in usage, of the Internet, for example, is due in large part to the development of devices and methods that simplify the actions a user must take to access multimedia information stored by network servers. One significant development is the use of hyperlinks which allows disparate pieces of information to be organized in nonsequential ways and which allows a user to easily navigate among the linked information. By assigning a unique identifier to each distinct piece of multimedia information available throughout a network, information can be readily accessed without regard to where it is stored. Network clients and servers participating in such a "hypermedia" network are referred to herein as hypermedia clients and hypermedia servers, respectively.
The Hypertext Transfer Protocol (HTTP) is one example of a method that implements hyperlinks and is probably the most widely used method for accessing the Internet today. A unique identifier, known as a Uniform Resource Locator (URL), specifies the location of a resource that can be accessed from the network.
HTTP clients and HTTP servers typically communicate with one another using any one of a family of communication protocols known collectively as Transmission Control Protocol/Internet Protocol (TCP/IP). One commonly used member of the family, known as Transmission Control Protocol (TCP), provides for a very reliable delivery of an information stream. According to the TCP, a sender establishes a "connection" with a receiver, transmits an information stream in basic units known as packets, and retransmits any packets that are either lost or corrupted during transmission. One advantage of the TCP is that it guarantees the receiver will receive the bits and bytes in the information stream in the correct order. Unfortunately, the TCP requires considerable computing and network bandwidth resources. The establishment of a connection, for example, may require an exchange of more than ten packets between sender and receiver.
In addition to the resources required to implement the TCP, the HTTP itself also requires considerable resources to format, process and display information. This is not a significant disadvantage in many situations because personal computers and other workstations with sufficient computing power, memory and display capabilities are readily available to implement the HTTP client function.
There is, however, a growing interest to provide access to hypermedia servers connected to networks such as the Internet through mobile devices, particularly handheld devices like wireless telephones. These devices are characterized by severe limitations in processing power, memory space, display size, and buttons or keys by which a user can request, view and manipulate information obtained from a hypermedia server. Furthermore, the bandwidth of the communication channels connecting the mobile devices to the rest of the network is also severely limited.
A wireless telephone has only a small fraction of the resources provided by a typical desktop or portable computer. Typically, the processing power is less than one percent of the processing power in many computers, the memory space is generally much less than 150 kilobytes (kB), and the display is perhaps four lines high and twelve or twenty characters wide. Graphics capabilities are very limited or nonexistent. The communication path is often in the range of 400 to 19,200 bits per sec. and the cost using that communication path is measured in terms of United States dollars per 100 kB or more.
Attempts to implement HTTP client functions in portable devices have not been very successful. Attempts that have used mobile devices providing facilities which are comparable to conventional computers are unattractive because the cost of the device is very high. Other attempts using less expensive devices are also unattractive because the client functions are severely limited. In either case, the communication delays and costs in exchanging packets with the network just to establish a connection, for example, are intolerable. The delays are particularly annoying in situations where a user is notified that electronic mail or other information has been received in the user's "mail box" somewhere on the network and the user must wait during the roundtrip delay required to request and receive that mail from the mail box. The usability of the device is further impaired because there is insufficient memory space to store lists of frequently used hyperlinks. For HTTP clients, these hyperlink identifiers are URLs that are often difficult to remember and difficult to enter into the device due to limited data entry capabilities. Two popular software products used in conventional computers refer to these stored hyperlinks as "bookmarks" and "favorites."